1. Field of the Invention
The invention concerns a method for feeding energy from photovoltaic modules of a photovoltaic system into a supply grid, or to a load, wherein the DC voltage generated by the photovoltaic modules is converted in an inverter with an intermediate circuit with a capacitor and with a DC/AC-converter into an AC voltage, and in a feed-in mode of operation the inverter is connected via a switching device to the supply grid, or to the load.
The invention furthermore concerns an inverter for converting the DC voltage generated by photovoltaic modules into an AC voltage for feeding into a supply grid, or to a load, with a control device, an intermediate circuit with a capacitor, a DC/AC-converter, and a switching device for connecting the output to the supply grid, or to the load, in a feed-in mode of operation, which is designed for executing the above method.
The present invention relates both to grid-connected photovoltaic systems, in which the electrical energy generated by the photovoltaic modules is fed into a supply grid, and also relates to so-called stand-alone inverters in which the energy delivered from the photovoltaic modules is used for a load, or for charging a battery.
2. Description of the Related Art
Methods and devices for connecting a photovoltaic system with a supply grid, or a load, have become of known art from, for example, DE 10 2010 060 633 B3 or EP 2 242 160 B1. In these, before the activation of the switching device of the inverter the input voltage of the inverter is determined. If the input voltage reaches a defined threshold value, the inverter initiates a switching-on procedure, in which the inverter, by activation of the switching device, is connected with the supply grid, or the load. The feed-in mode of operation, or the supply mode of operation, is then initiated at an operating point at which the maximum power is achieved (MPP: maximum power point). If, however, the photovoltaic system cannot deliver this input power, the inverter cannot maintain the feed-in mode of operation, or the supply mode of operation, and it deactivates the switching device such that the inverter is once again disconnected from the supply grid, or the load. This procedure is repeated until a feed-in mode of operation is possible, wherein the repetition takes place at relatively short intervals, so that the feed-in mode of operation can be executed as soon as possible after the conditions have been achieved. What is disadvantageous here is that the result is a high number of switching cycles, as a result of which the service life of the switching device is correspondingly reduced.